The present invention relates to a device for measuring vibration which is particularly useful for monitoring the operation of electrical equipment, although its usefulness is obviously not limited to this particular application.
In many instances, it is desirable to detect the occurrence of vibration and measure its amplitude, and to transmit the measurement to a remote location. In electrical equipment such as large generators, for example, it is desirable to monitor the machine to detect the occurrence of abnormal vibration in the stator windings, the stator core, or other parts of the machine. Fiber optics light guides provide a very desirable means for transmitting this information since they consist of glass fibers, which are insulating and are not affected by high voltages, magnetic fields, high temperature, or other environmental influences to which they may be subjected. It has been proposed heretofore to measure vibration by the use of such light guides. Two fiber optics light guides have been used for this purpose, one serving as a light source which transmits light to the point of measurement and the other light guide being a receiver and transmitting the information to a remote location. The two light guides are arranged so that light from the source is received by the receiver, and a vibrating member, or a vane attached to such a member, is placed in position to extend across the light path between the source and the receiver in such a manner that movement of the vane varies the amount of light received by the receiver which can be transmitted to a remote location. Measurement of the amount of light thus received can be used to determine the occurrence and amplitude of the vibration.
Various devices of this general type are known and may be arranged so that the light transmitted from the light source either crosses the path of a moving vane or is reflected from the vane into the receiving light guide. In either case, the amount or intensity of light transmitted by the receiving light guide is determined, usually by converting it to an electrical signal, and can be used as an indication of the amplitude of movement of the vane. Such a system, however, has serious limitations. Thus, it can be used only to measure amplitudes which are comparable to the diameter of the light guide. A more serious deficiency of such a system is that any change in the intensity of the light source from which the light signal is obtained, or in the sensitivity of the electrical detection means, or in the optical transmission characteristics of the light guides, results in a change in the amount of observed light and thus causes an erroneous measurement.